Why There Have to Be "Pesky" Bugs

On weekday mornings I wait with our 5-year-old twins at the bus stop for kindergarten where a couple of neighbor boys wait for the same bus. The other kids are older, the sons of a pastor and his wife who live a few houses down from us. One morning last week the younger neighbor boy pointed out a beautiful spider web that was hanging dramatically, suspended in the air between some bushes and a telephone pole.

He then reached down to get a stick and was about to knock the web down, when his older brother gently told him to stop. "God made spiders," he explained.

I thought that was nice but it also opened up the question of why nature's design -- whether or not you think of God as the source of that design -- includes some arthropods like spiders that many of us find less than cuddly, and what purpose there could be behind a variety of insects that are equally if not more bothersome. My own kids have asked questions along these lines -- "Why do there have to be mosquitoes?" Whether in scientific or religious terms, I've lacked a compelling response. Until now, thanks to the National Science Foundation.

At first blush, many people would probably love to get rid of insects, such as pesky mosquitoes, ants and roaches. But a new study indicates that getting rid of insects could trigger some unwelcome ecological consequences, such as the rapid loss of desired traits in plants, including their good taste and high yields.

Specifically, the study -- described in the Oct. 5, 2012 issue of Science and funded by the National Science Foundation -- showed that evening primroses grown in insecticide-treated plots quickly lost, through evolution, defensive traits that helped protect them from plant-eating moths. The protective traits lost included the production of insect-deterring chemicals and later blooms that gave evening primroses temporal distance from plant-eating larvae that peak early in the growing season.

These results indicate that once the plants no longer needed their anti-insect defenses, they lost those defenses. What's more, they did so quickly -- in only three or four generations.

Anurag Agrawal, the leader of the study and a professor of ecology and evolutionary biology at Cornell University, explains, "We demonstrated that when you take moths out of the environment, certain varieties of evening primrose were particularly successful. These successful varieties have genes that produce less defenses against moths."

In the absence of insects, the evening primroses apparently stopped investing energy in their anti-insect defenses, and so these defenses disappeared through natural selection.

So the "evolution" for which there is now "hard evidence" amounts merely to the loss of a function. Take away the insects, and evening primroses lose their ability to deter insects. This is something we also knew already: evolution observed experimentally may include the degrading of function. It does not include the building up of complex new functionality. The latter appears to require direction from a source of intelligent design.

Much more interesting is the observation that many of the properties we enjoy in plants -- as food, in pharmaceuticals and herbal remedies -- are qualities that plants have in the first place because they serve as defenses against insects:

Agrawal believes that his team's study results are applicable to many other insect-plant interactions beyond evening primroses and moths. Here's why: The ubiquitous consumption of plants by insects represents one of the dominant species interactions on Earth. With insect-plant relationships so important, it is widely believed that many plant traits originally evolved solely as defenses against insects. Some of these anti-insect plant defenses, such as the bitter taste of some fruits, are desirable.

[...]

"One of the things farmers are trying to do is breed agricultural crops to be more resistant to pests," said Agrawal. "Our study indicates that various genetic tradeoffs may make it difficult or impossible to maintain certain desired traits in plants that are bred for pest resistance."

In addition, oils produced by evening primroses have been used medicinally for hundreds of years and are beginning to be used as herbal remedies. Agrawal's insights about pests that attack these plants and about chemical compounds produced by these plants may ultimately be useful to the herbal and pharmaceutical industries.

There's a Darwinian explanation for this: Insects and plants' anti-insect defenses evolved together, with all those wonderful properties that plants offer us being no more than the extremely lucky product of happenstance. But ID's explanation is more satisfying because it doesn't rely on luck. In a view of nature informed by the theory of intelligent design, it seems reasonable to think that plants taste good and are useful in medical remedies because that is part of a vision of how things should be, a vision proceeding from a purposeful plan.

Plants evidently need many those same properties as part of their strategy of self-defense against insects. This was true long before there were human being around to enjoy plants. So you see how insects, including some rather uncharismatic ones, play their indispensable role. This, I think, is how I would answer my kids. It makes sense to me, an adult, as well.